In terms of compression they are obviously the same at 85mm. The 70-200 would give you more compression at the longer end. Still, f/1.8 gives a lot shallower DOF than 2.8, so if that is what you are after it's hard to go wrong with the 85 1.8G, which is so well priced. It is also as you say a lot easier to carry around than a 70-200.